Carrier current relay

ABSTRACT

The disclosed bistable relay has a bistable switch operable into either stable state from the other by an actuator comprising two bimetals arranged to defect in opposite directions due to selective heating. The switch-actuating ends of the bimetals are constrained to deflect together and yet they can slide in relation to each other. Brief selective energization of heaters causes operation of the relay - and the switch - in opposite directions. Thereafter the switch remains set, and the bimetals compensate mutually for ambient temperature variations. The common mount of both bimetals is adjustable for proper relationship between the actuating bimetals and the bistable switch.

United States Patent [191 Thorsteinsson [451 May 22, 1973 CARRIER CURRENT RELAY 22 Filed: Sept. 30, 1971 211 Appl.No.: 185,036

[52] US. Cl. ..337/335, 337/101, 337/104 [51-] Int. Cl. ..H0lh 37/52 [58] Field of Search ..337/38, 49, 94, 95, 337/96, 101, 104,112, 335, 336, 102

[56] References Cited UNITED STATES PATENTS 2,769,890 1l/l956 Hallerberg et a1 ..337/l04 X 2,284,383 5/1942 Elmer ..337/94 X FOREIGN PATENTS OR APPLICATIONS 568,982 11/1957 ltaly ..337/335 828,876 1/1952 Germany ..337/94 Primary Examiner-Bernard A. Gilheany Assistant Examiner-1 E. Bell Att0rney-Paul S. Martin [5 7] ABSTRACT The disclosed bistable relay has a bistable switch operable into either stable state from the other by an actuator comprising two bimetals arranged to defect in opposite directions due to selective heating. The switch-actuating ends of the bimetals are constrained to deflect together and yet they can slide in relation to each other. Brief selective energization of heaters causes operation of the relay and the switch in opposite directions. Thereafter the switch remains set, and the bimetals compensate mutually for ambient temperature variations. The common mount of both bimetals is adjustable for proper relationship between the actuating bimetals and the bistable switch.

3 Claims, 1 Drawing Figure CARRIER CURRENT RELAY This invention relates to a bistable thermal relay which is compensated against changes in ambient temperature. The relay may be changed from an ON condition to an OFF condition, or vice versa by changing the temperature of one or other of a pair of bimetals.

Thermally operated relays are known to those skilled in the art of electrical switching. Such relays have not been capable of precise setting of the change-over adjustment due to lack of thermal compensation and due to significant changes in geometry accompanying temperature changes.

It is an object of one aspect of the invention to provide a thermally operated bi-stable relay which is compensated for changes in ambient temperature.

In accordance with the foregoing object, the illustrative embodiment of the invention described in detail below comprises a snap-switch having first and second stable states corresponding to open and closed switch conditions and an operator for moving said switch from one to the other of said stable states. An actuator for the switch operator includes two bimetals arranged in thermo-expansive opposition to each other with one pair of adjacent ends fixed to a common mount. The other pair of adjacent ends of the bimetals are movable, being slidably joined together and arranged to deflect in unison in response to heating or cooling of one of said bimetals relative to the other of said bimetals. The movable bimetal ends are substantially motionless when both bimetals are exposed to equal heating or cooling. The movable pair of adjacent bimetal ends are disposed adjacent to and operable upon said switch operator. Means is provided for adjusting the common mounting of the bimetals-in relation to said snap-switch for establishing a datum position for the movable pair of bimetal ends.

The accompanying drawing is a side view of a bistable thermal relay, shown partly in cross-section, as an illustrative embodiment of the invention.

Referring to the drawing, a switch frame, generally indicated at 1 carries a micro-switch 2 having an operator 5. The microswitch 2 normally has one stable and one state that is unstable in the sense that pressure on operator is needed to maintain that state. In its stable state, the movable switch arm 2a engages fixed contact 2b, and over-centering spring provides spring bias tending to hold switch arm 2a in that position. Switch operator 5 is leftward of the position shown. When operator 5 is pressed toward the right, arm 2a. is operated by spring 2c to snap into the position shown, the nominally unstable state. Two stable states exist after assembly and calibration of the relay as a whole. The switch is a typical snap action type and the precise details of the switch form no part of the present invention.

A cantilevered mounting 8, fastened to or fixed relative to the frame 1, is slightly resilient and movable under the action of an adjusting screw 7. The mounting 8 is fixed to an end of each of the two bimetal elements 3 and 4. Bimetals 3 and 4 (viewed edgewise) are spaced apart and substantially parallel throughout their lengths. One pair of bimetal ends are firmly joined together adjacent the mounting 8. The opposite pair of bimetal ends are movable, and they are slidably joined together by tying element 6 to deflect in unison. The movable end of bimetal element 3 is operable upon the operator 5.

Bimetals 3 and 4 are assembled so to be thermoexpansive in opposition to one another. In the form shown, each bimetal is formed of dissimilar metals, both bimetals have the same thermal deflection characteristic and they are arranged so that they tend to deflect in opposite directions when both are heated or cooled. Accordingly, there is no change in the position of the movable ends of the bimetals when the temperature of both of them changes equally. For a given change in ambient temperature, the deflection force produced by one bimetal is equal and opposite to the deflection force produced by the other bimetal. The bimetal 4 is heated selectively or predominantly by heater 10 and bimetal 3 is heated selectively or predominantly by heater 9. Thus heating (or cooling) of one bimetal without heating (or cooling) of the other bimetal will actuate the switch. The heaters may be electrically resistive, or inductive, and the bimetals may be arranged to carry heating current, and the bimetals may be actuated by thermoelectric devices in lieu of heaters.

The thermal relay shown has two stable states by virtue of a precise setting of the datum position of those ends of the bimetals that are fixed to mounting 8. Adjuster 7 acts to tilt the mounting 8 when the adjustor is screwed deeper into frame 1, and the resilience of mounting 8 causes reverse tilting when the adjusting screw 7 is backed out. Two stable states of the relay are established by adjusting the bimetal mounting so that the active or movable ends of the bimetals bear with sufficient pressure against the operator 5 via the bimetals 3 and 4 to cause the snap-switch to be capable of remaining indefinitely in either the nominally on state as shown, with switch arm 2a engaging contact 2d, or the off state, which ever it happens to be in at any given time.

The pressure of the bimetals acting on the operator 5 is equal to the mean of (1) the force required to operate the switch out of its usual stable state and (2) the release force of snap switch 2, that is, the spring bias applied by switch arm 2a against operator 5 when the switch is held in the position shown.

In use, one of the heaters 9 or 10 is energized briefly, causing the switch to snap from one state to the other. Interruption of the heater energization does not change the condition of the switch. The other heater is energized briefly to change the switch to its other stable state. Once again, deenergizing the second heater does not affect the switch, which remains in its last-operated state.

The bimetals have matched thermal deflection characteristics and they are arranged to deflect in opposite directions when individually heated. Consequently, when both bimetals are heated alike and when both are cooled alike, the movable ends (constrained by element 6 to deflect in unison) do not move in response to ambient temperature changes.

Other embodiments of the invention will occur to those skilled in the art.

I claim:

1. A temperature compensated bi-stable thermally operated relay comprising i. a snap-switch having first and second stable states and an operator for moving said switch from one to the other of said stable states,

ii. a thermal actuator including stationary mounting means, two bimetals arranged in thermo-expansive opposition to each other, said bimetals having one pair of ends adjacent each other and fastened to said stationary mounting means, said bimetals having another pair of ends adjacent each other and constrained to deflect in unison, said other ends both being movable in response to a temperature difference between said bimetals, and said movable ends of said bimetals remaining at rest when the bimetals are exposed to equal temperature changes, said thermal actuator including separate electric heaters for said bimetals, and

iii. means including said operator forming a mechanical operating connection from said movable bimetal ends to said snap-switch, the whole being adjusted so that said snap-switch tends to remain in the last state to which it was actuated in response selective temporary heating of one of the bimetals, despite later equalization of the temperatures of the bimetals.

2. A thermally operated relay in accordance with claim 1, wherein said snap-switch of itself tends to assume one stable state and pressure against said operator is required to position the snap switch in its other stable state, and wherein the whole is adjusted to cause the movable ends of the bimetals to act jointly in applying that amount of pressure to said operator to cause the switch to remain in said other stable state after being operated thereto, in the absence of unequal temperatures of the bimetals.

3. A thermal relay in accordance with claim 1, wherein said mounting means is a resilient support for said fastened ends of said bimetals and including adjustment means arranged to impose positive deflection on said mounting means in one direction, the resilient mounting means causing controlled reverse adjustment of the fastened ends upon controlled retraction of said adjustment means. 

1. A temperature compensated bi-stable thermally operated relay comprising i. a snap-switch having first and second stable states and an operator for moving said switch from one to the other of said stable states, ii. a thermal actuator including stationary mounting means, two bimetals arranged in thermo-expansive Opposition to each other, said bimetals having one pair of ends adjacent each other and fastened to said stationary mounting means, said bimetals having another pair of ends adjacent each other and constrained to deflect in unison, said other ends both being movable in response to a temperature difference between said bimetals, and said movable ends of said bimetals remaining at rest when the bimetals are exposed to equal temperature changes, said thermal actuator including separate electric heaters for said bimetals, and iii. means including said operator forming a mechanical operating connection from said movable bimetal ends to said snap-switch, the whole being adjusted so that said snap-switch tends to remain in the last state to which it was actuated in response selective temporary heating of one of the bimetals, despite later equalization of the temperatures of the bimetals.
 2. A thermally operated relay in accordance with claim 1, wherein said snap-switch of itself tends to assume one stable state and pressure against said operator is required to position the snap switch in its other stable state, and wherein the whole is adjusted to cause the movable ends of the bimetals to act jointly in applying that amount of pressure to said operator to cause the switch to remain in said other stable state after being operated thereto, in the absence of unequal temperatures of the bimetals.
 3. A thermal relay in accordance with claim 1, wherein said mounting means is a resilient support for said fastened ends of said bimetals and including adjustment means arranged to impose positive deflection on said mounting means in one direction, the resilient mounting means causing controlled reverse adjustment of the fastened ends upon controlled retraction of said adjustment means. 